Fast magnetic reconnection in a kinked current sheet

Abstract

Magnetic reconnection processes in a kinked current sheet are investigated using three-dimensional electromagnetic particle-in-cell simulations in a large system where both the tearing and kink modes are able to be captured. The spatial resolution is efficiently enhanced using the adaptive mesh refinement and particle splitting-coalescence method. The kink mode scaled by the current sheet width such as kyL∼1 is driven by the ions that are accelerated due to the reconnection electric field in the ion-scale diffusion region. Although the kink mode deforms the current sheet structure drastically, the gross rate of reconnection is almost identical to the case without the kink mode and fast magnetic reconnection is achieved. The magnetic dissipation mechanism is, however, found very different between the cases with and without the kink mode. The kink mode broadens the current sheet width and reduces the electron flow velocity, so that the electron inertia resistivity is decreased. Nevertheless, anomalous dissipation through the electron thermalization compensates the decrease in the inertia resistivity so as to keep a high reconnection rate. This suggests that the electron dynamics in the electron diffusion region is automatically adjusted so as to generate sufficient dissipation for fast magnetic reconnection. The electron thermalization occurs effectively because the electron meandering scale along the current sheet is comparable to the wavelength of the kink mode. On the other hand, two-dimensional simulations in the plane orthogonal to the magnetic field shows that in higher mass ratio cases with mi/me>100 the electron thermalization is caused due to a hybrid-scale mode with wavelength intermediate between the ion and electron inertia lengths kyλiλe∼1 rather than the large-scale kink mode with kyL∼1, because the electron meandering scale is shortened as the mass ratio increases.

The inversion layer of electric fields and electron phase-space-hole structure during two-dimensional collisionless magnetic reconnection

“…In the vicinity of the X line, the force balance on a differential volume of electrons is expressed as −en e E z ϳ ‫ץ‬P exz / ‫ץ‬x + ‫ץ‬P eyz / ‫ץ‬y, where P exz and P eyz are the off-diagonal electron pressure-tensor components. 2,27,35 As further shown in Fujimoto ͑2009͒ and consistent with our PIC result, ͉‫ץ‬P exz / ‫ץ‬x͉ ӷ ͉‫ץ‬P eyz / ‫ץ‬y͉. Figures 6͑a͒ and 6͑b͒ show the forces −en e E z and −‫ץ‬P exz / ‫ץ‬x multiplied by V ez at time T3.…”

Relativistic magnetic reconnection in collisionless ion-electron plasmas explored with particle-in-cell simulations

“…Second, we find larger rates for the relativistic setups (0.18−0.25) than for the mildly relativistic case (0.15). These rates are also larger than those reported in the literature for ion-electron non-relativistic reconnection (0.07−0.15 for Birn et al 2001;Pritchett 2001;Fujimoto 2006Fujimoto , 2009Daughton et al 2006;Klimas et al 2010). This points toward relativistic reconnection being slightly faster than non-relativistic reconnection.…”

“…The thermal inertia term k ∂ k (n e δp k δv y ) is slightly positive, and partly cancels the contribution of bulk inertia. This cancellation is also reported in Fujimoto (2009) and Klimas et al (2010) for non-relativistic ion-electron plasmas, and in Bessho & Bhattacharjee (2012) for relativistic pairs. Only ∂ x (n e δp x δv y ) contributes and is negative, which is easily seen when looking at the temperature curves T xy,e and T zy,e (Fig.…”

“…For example, Fujimoto (2009) reports E * = 0.15 for m i /m e = 100 and 0.08 for pairs. Liu et al (2014) report close rates for m i /m e = 1 and 25.…”

“…The literature concerning 2D non-relativistic reconnection largely shows that for antiparallel reconnection, the dominant term is thermal inertia either in ion-electron (Klimas et al 2010;Shay et al 2007;Fujimoto 2009) or pair (Bessho & Bhattacharjee 2005) plasmas, and this is the key element of various analytical models (e.g., Hesse et al 2011). On the other hand, reconnection with a guide field is sustained by electron bulk inertia on skin-depth scales, and thermal inertia on Larmor radius scales (Hesse et al 2002(Hesse et al , 2004Liu et al 2014).…”